Wood is a highly flammable material used in many forms and configurations in construction of residential, commercial, and industrial structures. To decrease the flammability of products made from wood, fire retardants have been incorporated into the wood. For instance, polymer resins have been impregnated into the wood to improve its flame retardance and also to improve the strength, hardness, coloring, and useful lifetime of the wood. Such polymer resins include melamine-formaldehyde resins, urea-formaldehyde resins, and melamine-urea-formaldehyde resins.
Urea-formaldehyde resins are known in the art to be inexpensive and provide good thermal properties, excellent hardness, and an absence of color change to the treated wood. However, once cured, the urea-formaldehyde resins are susceptible to acid hydrolysis upon contact with water, resulting in the release of formaldehyde, which is toxic. To increase the durability of the wood, making it less likely to hydrolyze, melamine (1,3,5-triazine-2,4,6-triamine)-formaldehyde resins have been used. While melamine-formaldehyde resins are more heat resistant, less susceptible to acid hydrolysis, and more water resistant than urea-formaldehyde resins, the melamine-formaldehyde resins are more expensive to manufacture. Melamine-urea-formaldehyde resins have the desirable properties of urea-formaldehyde resins and melamine-formaldehyde resins: the cost-effective, urea-formaldehyde component and the hydrophobic, durable properties of the melamine-formaldehyde component. When compared to a urea-formaldehyde resin, a melamine-urea-formaldehyde resin is more durable and hydrophobic and emits less formaldehyde.
Phosphazene compounds have been used to improve the flame retardance of polymeric substrates, such as wood or textiles. The phosphazene compound is mixed or blended with the polymeric substrate. Phosphazene compounds have also been reacted with the polymeric substrate to improve its flame retardance. For instance, N-methylol phosphazene compounds have been reacted with cellulosic materials or polymers to provide flame retardance.